Star Wars-like holograms: 3D images that float in thin air

In the original Star Wars film, R2D2 projects an image of Princess Leia in distress. The scene includes the iconic line: “Help me Obi Wan Kenobi, you're my only hope.”

Brigham Young University (BYU) electrical and computer engineering professor and holography expert Daniel Smalley has long had a goal to create the same type of 3D image projection. Now, Prof Smalley details the method he has developed to do just this.

“We refer to this colloquially as the Princess Leia project,” he said. “Our group has a mission to take the 3D displays of science fiction and make them real. We have created a display that can do that.”

Firstly, Prof Smalley explained, the image of Princess Leia is not a hologram. A 3D image that floats in air, that you can walk all around and see from every angle, is actually called a volumetric image.

A holographic display scatters light at a 2D surface, so if you aren’t looking at that surface you won't see the 3D image. A volumetric display has little scattering surfaces spread throughout the 3D space occupied by the 3D image, meaning that a volumetric image can be seen from any angle.

Prof Smalley and his colleagues have devised a free-space volumetric display platform, based on photophoretic optical trapping, that produces full-colour, aerial volumetric images with 10μm image points by persistence of vision.

The optical trapping technology used to create the images is a highly focussed laser beam containing a strong electric field gradient that can be used to manipulate microscopic particles.

Prof Smalley’s team used near-invisible lasers to trap a tiny particle of cellulose, heating it unevenly to move it around in the air. Meanwhile, a second set of red, green and blue lasers illuminates it.

If the particle moves fast enough, your eye sees it as a line. In this way, the researchers were able to create 3D light animations in the air. They’ve called it the Optical Trap Display, and the device itself is the size of a lunch box.

Prof Smalley said the easiest way to understand what they are doing is to think about the images they create like 3D-printed objects.

“This display is like a 3D printer for light,” Smalley said. “You're actually printing an object in space with these little particles.”

So far Smalley and his student researchers have 3D-light printed a butterfly, a prism, the BYU logo, rings that wrap around an arm and an individual in a lab coat crouched in a position similar to Princess Leia as she begins her projected message.

While previous researchers outside of BYU have done related work to create volumetric imagery, Prof Smalley’s team is the first to use optical trapping and colour effectively. Their method of trapping particles and illuminating it with colourful lasers you can see is novel and they believe that it is scalable with the scope to create larger images.

“We’re providing a method to make a volumetric image that can create the images we imagine we'll have in the future,” Smalley said.